Despite the use of aggressive surgical resection and chemotherapy, nearly 50% of patients with colorectal carcinoma, the 3rd deadliest cancer in the US, will develop recurrent disease, highlighting the need for improved therapies. The failure to produce long-term clinical remission in CRC patients could reflect the inability to target cancer stem or stem-like cells (CSCs/CSLCs; that express cancer stem cell markers) efficiently since these cells are known to be resistant to conventional therapies. Differentiation therapy, which results in loss of self-renewal and induction of terminal differentiation or apoptosis in CSLCs, may be a valid option for the treatment of recurrent colorectal cancer. We have shown that miR-21, an emerging oncogene which induces stemness by activating Wnt/-catenin and EGFR signaling in colon cancer cells stimulates tumor promotion, invasion and metastasis. miR-21 is also greatly elevated in 5-FU + Oxaliplatin (FUOX) resistant colon cancer cells; downregulation of miR-21 leads to differentiation of these cells, as evidenced by increased CK-20 expression and alkaline phosphatase activity. Moreover, this downregulation renders the FUOX-resistant colon cancer cells susceptible not only to FUOX but also to 3, 4-difluorobenzo-curcumin or difluorinated curcumin (CDF) and the combination of CDF and FUOX. CDF is a novel analog of the dietary ingredient curcumin with much greater bioavailability and growth inhibitory properties than the parent compound. Additionally, we have observed that in response to CDF or the combination CDF and FUOX, miR-21-downregulated FUOX-resistant colon cancer cells exhibit decreased expression of EGFR and CD44 and increased apoptosis. CDF alone and the combination of CDF and FUOX were much more effective than FUOX alone. We propose to extend this differentiation therapy in a preclinical setting. Therefore, we will use SCID mice xenograft and orthotopic models of colon cancer to test the hypothesis that down regulation of miR-21 by antagomir-21 (antisense miR-21) in chemotherapy surviving colon tumors will lead to differentiation of chemotherapy-resistant tumor cells known to be enriched in CSCs/CSLCs. We further hypothesize that while subsequent treatment with FUOX will only be partially effective in obliterating the refractory colon tumors, treatment with either CDF or the combination of CDF and FUOX will be highly effective in causing a complete or near complete regression of the tumor by killing differentiating chemo-resistant colon CSCs/CSLCs through inhibition of Wnt/-catenin and EGFR signaling. Finally, we will demonstrate that miR-21 regulates -Wnt/catenin and EGFR signaling pathways in colon cancer chemo-resistant cells in vitro.